1) Scene in the GFII boathouse when Michael tells Fredo "your nothing to me now, not a brother, not a friend, I don't want to know you or anything you do".
2. Vito's revenge killing of Don Ciccio. I thought it was just an awesome scene.
3. Scene in Godfather 3 when Michael says the infamous line "just when I thought I was out they pull me back in"